1. Field of the Invention
This invention relates to a preloadable retainer for fastening two planar objects together. In particular, the invention relates to a fastener comprising an anchor and a push pin that is particularly useful for fastening automotive body panels to sheet metal.
2. The Prior Art
Anchor type fasteners having a central pin are known. For example, U.S. Pat. No. 4,571,134 to Beglinger et al. shows a two-piece plastic fastener comprising an anchor and a central pin. The anchor comprises a closed V-shaped insertion portion and a top plate. The anchor is placed through two (or more) planar items to be fastened together. A central pin extends down between the arms of the V and causes the arms to spread when the pin is fully depressed. This spreading anchors the fastener in the rear item and prevents the fastener from coming out. The plate prevents the front item from coming away from the rear item. While this type of fastener is widely used, the closed V-shape of the anchor makes it difficult to install. This is because a large amount of force is required to cause the arms of the V to bend inward sufficiently to pass through an aperture in the item to be mounted, and outward sufficiently enough to let the pin extend to its fully inserted position and retain the anchor in the item. The anchor must bend enough during insertion of the pin so as to prevent the anchor from being inadvertently pulled out by a counter force acting on the items.
Other fasteners using the same concept are shown in U.S. Pat. Nos. 6,533,515, 6,074,144 and 5,775,860 all to Meyer, as well as U.S. Pat. No. 6,045,309 to LeVey. These fasteners all suffer the same drawback as Beglinger: the closed V formation of the anchor is so resistant to bending that a large amount of force is required to insert the fastener, and bring it into a locked position.
A plastic fastener having a different configuration is shown in U.S. Pat. No. 4,085,651 to Koscik. In this fastener, the anchor consists of two parallel legs that extend below the plate. Depressing the center pin forces the legs to bend outwards and retain the fastener in the item. This fastener suffers the drawback that the parallel legs are more difficult to insert into a small aperture in the item, as they must often be squeezed together by the operator's fingers in order for the anchor to be inserted.
In large capacity use, such as automobile assembly lines, it is imperative that the fasteners used to attach body panels to the automobile frame be quick and easy to install in large quantities. Since the fasteners are inserted by hand, they should not require undue force to complete the insertion, due to operator fatigue. They should also be able to be installed using a minimum number of steps.